The contactless power transmission in which the power is supplied without using a power cord is attracting attentions. The conventional contactless power transmission is mainly the type based on the electromagnetic induction. It is expected that this technique can be applied to various fields.
In view of the circumstance shown above, such a project is being studied that an electric vehicle is provided with a power receiving coil at its bottom part (power receiving side) and a high power (for example, several kilowatt to several tens of kilowatt) is transmitted in a contactless manner from a power feeding coil on the ground (power feeding side). If the contactless power transmission can be utilized, then the power can be transmitted without mechanically coupling power feeding side to power receiving side.
However, if some foreign matter are present in the gap between the power feeding coil and the power receiving coil when the power is being transmitted in a contactless manner, concerns rise that when the foreign matter is a metal, an eddy current will generate due to the magnetic flux passing through the foreign metal, and when the foreign matter is a magnetic body, there will be a hysteresis loss due to the magnetic flux passing through the foreign magnetic body, so that the foreign matter may be heated.
As a way to avoid the heating problem, Patent Document 1 has suggested a detecting apparatus with a detecting part. Specifically, the detecting part is provided with one or a plurality of magnetic coupling elements which is/are composed of a plurality of coils. It measures the electric parameters related to the magnetic coupling element(s) or a circuit containing at least the magnetic coupling element(s) and then determines whether a foreign matter that may generate heat due to the magnetic flux is present based on the changes of these electric parameters.